The following relates generally to transmitting information between an intended source and a receiver in a communication system, and more particularly to designs for frequency reuse and pilot subcarriers to minimize co-channel interference during transmission from other sources that cause interference.
There are several conventional techniques to increase the throughput of a wireless network. These techniques aim to expand the amount of information that can be transmitted over the network while minimizing the probability that errors will occur during transmission. One of these techniques is frequency reuse, which entails using the same frequency on a network for multiple simultaneous transmissions. Most wireless communication systems are designed to achieve a frequency reuse of one, which is often referred to as the “universal” frequency reuse factor. A frequency reuse of one means that the source, or base station, for each cell in the network uses the same set of frequencies simultaneously for the transmission of information. However, in wireless systems it is challenging to achieve a frequency reuse of one because of the co-channel interference presented by the sources of adjacent cells. Thus, separate communication techniques may be used in the transmission of information in order to differentiate the information transmitted by the source in each cell.
One of the techniques used to reduce co-channel interference is orthogonal frequency-division multiplexing (OFDM). OFDM is a digital multi-carrier modulation scheme which uses a large number of closely-spaced subcarriers comprised of an orthogonal set of data symbols to transmit information. These subcarriers typically overlap in frequency, but are separated using algorithms such as a Fast Fourier Transform. Each subcarrier is typically modulated with a conventional modulation scheme, such as quadrature amplitude modulation or amplitude and phase-shift keying, in order to maintain a data rate similar to a single-carrier modulation scheme.
Traditional OFDM requires estimating the channel to determine co-channel interference between sources. However, in order to determine the interference between sources, one must know the parameters of the channel used for transmission. This requisite knowledge presents a problem for cellular communication systems—achieving a frequency reuse of one results in co-channel interference that makes it harder to estimate the parameters of the channel, while using a multi-carrier modulation scheme such as OFDM to eliminate the co-channel interference requires knowing the parameters of the channel.